2011 AIPMT-MAINS Moving Charges and MagnetismMagnetic Field due to a Circular Coil Easy Question 10 of 15 in Magnetic Field due to a Circular Coil

Charge q is uniformly spread on a thin ring of radius R. The ring rotates about its axis with a uniform frequency f Hz. The magnitude of magnetic induction at the center of the ring is

A $\frac{\mu_0q}{2\pi fR}$
B $\frac{\mu_0qf}{2\pi R}$
C $\frac{\mu_0qf}{2R}$
D $\frac{\mu_0q}{2fR}$

The answer is C.

Solution

A rotating charged ring is equivalent to a circular current loop.
The charge q passes any point f times per second, so the current is $I = \frac{q}{T} = qf$
Magnetic field at the centre of a circular loop of radius R: $B = \frac{\mu_0I}{2R}$
$B = \frac{\mu_0qf}{2R}$

Concept Current due to rotating charge

Magnetic Field due to a Circular Coil in past papers

15 questions from this chapter have appeared across 12 exam years.